PCA would never send "SPAM" of any sort or junk mail, it would be entirely against their principles.
I do receive survey forms and e-mails alerting me to the latest issues or anything they think may be of interest but this was at my request.
I'm sure the reason for this happening is because you chose not opt out of the mail from IDG companies or their associates on signing up. [This can be changed from your personal details] or as above you may have entered a competition and ticked or un-ticked the relevant box regarding them contacting you. This also can be changed.
FE will I'm sure, explain much better than I can why or how this may have happened. j.